1. Field of the Invention
This invention relates to an underbody structure for a vehicle, and more particularly to an underbody structure for mounting a fuel tank for a vehicle in which the fuel tank is disposed at the rear thereof.
2. Description of the Prior Art
In rear-engine rear-drive (RR) vehicles and midshipengine rear-drive (MR) vehicles, location of the fuel tank has been a difficult and important problem. For example, when the fuel tank is located between the engine and the passenger compartment, the size of the passenger compartment is decreased by the space taken up by the fuel tank and fuel in the fuel tank is apt to foam due to heat from the engine and cause detonation of the engine during motion. On the other hand, when the fuel tank is located at the front of the vehicle body or in the side sills, there arises a problem with safety that if the vehicle has a head-on or side collision, the fuel tank is liable to be broken.
In Japanese Unexamined Patent Publication No. 57(1982)-201722, to locate the fuel tank in RR type cars or MR type cars, it is proposed to utilize the tunnel portion which extends longitudinally in the center of the floor in front-engine rear-drive (FR) type cars to house a propeller shaft but is not necessary in RR type or MR type cars having no propeller shaft like that of the FR type car. This arrangement is advantageous in that the fuel tank can be disposed in the center of the vehicle body in which there is less possibility of breakage of the fuel tank upon collision. However, the arrangement cannot be considered to be optimal from the viewpoint of the space in the passenger compartment since the tunnel portion projects into the passenger compartment to reduce the space therein. Especially in small cars, the influence of the tunnel portion on the space in the passenger compartment is significant.